Diagnosis and the identification of accurate biomarkers for diseases, including diseases of the human brain, are needed to improve early detection and prognosis. Imaging markers for neurodegenerative diseases have recently become clinically relevant. For example, “Pittsburgh compound B,” a fluorescent analog of thioflavin, may be used in imaging beta amyloid plaques in Alzheimer disease (Klunk et al., “Imaging Brain Amyloid in Alzheimer's disease with Pittsburgh Compound-B,” Ann. Neurol. 55: 306-19 (2004); Price et al., “Kinetic Modeling of Amyloid Binding in Humans using PET imaging and Pittsburgh Compound-B,” J. Cereb. Blood Flow Metab. 25: 1528-47 (2005). An injection of loflupane I123 with subsequent imaging using single positron emission tomography (SPECT), also known as DaTscan (Hauser R A, Grosset D G, [123I]FP-CIT (DaTscan) SPECT Brain Imaging in Patients with Suspected Parkinsonian Syndromes. J. Neuroimaging (2011)); XX:1-6), may be used to detect individuals with Parkinsonian disorders and is currently in clinical use to help differentiate causes of symptoms in individuals with suspected neurodegenerative Parkinsonism but equivocal clinical findings.
Both of these biomarkers use a known feature of a particular disorder, such as the deposition of a particular matrix of proteins (beta-amyloid plaques) or a regional reduction in binding of dopamine, to identify individuals with a particular disorder. Imaging biomarkers of this type generally use a specific property of an injected tracer to identify a subject with a particular disorder. These methods are by their nature limited to diagnosis or evaluation of a specific disorder in question and do not generally have broader applicability to answer other questions.